To solve this, think about it as 17 is 4 out of 10 total parts of a number. So if the whole number has 10 parts, 4 of the parts equals 17, another 4 of the parts is another 17, and then we just have two parts left over. Those parts are equal to half of 17, which is 8.5.
Therefor the whole number is 17+17+8.5, which is 42.5.
